"BOEING377" wrote in message
...
Are zap stoppers really needed on alternators? These aftermkt devices
claim to
portect alt. diodes against damage from transients. I can't imagine that
engineers at places like Motorola would design alternators that needed
external
aftermarket devices to effectively protect them from transients. I have
never
blown up an alternator from switching it in and out of a load, although
people
say this is often fatal to the diodes. I have run alternators open circuit
(no
load at all) with no problems. Was I just lucky?


The fault conditions of a vehicle electrical system are very well known.
Good engineering practice dictates that the item you design should withstand
all normal operating conditions, plus those conditions generated by a single
fault, or even multiple faults. How long your device survives, and how many
multiple fault conditions it will tolerate, is controlled by economics.

Running the engine while the battery lead is disconnected is certainly a
single-fault (and reasonably likely to occur) condition. I know I have done
this rather often, and I have never had any associated failures. OTOH, it
has always been done with GM autos with internal regulator alternators. So,
however they do it, the GM engineers have designed-in a control over that
single-fault condition.

Notice that I said a "control" and not a "tolerance". In the "no battery"
single-fault condition, the alternator will supply the vehicle electric
power load. If the loss of the battery allows for the alternator to create a
vastly over-voltage condition, then protection would have to be designed
into every electrical load device. It's a lot easier to just control the
alternator output voltage.

From my experience, the alternator is one of the most reliable parts of your
car. Almost everything wears out or needs service before the alternator. If
your alternator fails, I think you must be exceptionally unlucky, or very
creative in producing a really unusual fault condition.


Ed